Many of the compounds which have been used as a flavor component, a fragrance component or a flavor-improving agent in beverages, foods, cosmetics, etc., are racemic forms. For example, S-alkyl 2-methylbutanethioates are known to be present as racemic forms in natural products, particularly in fruits and beer (non-patent literatures 1 to 13). Of these racemic S-alkyl 2-methylbutanethioates, S-methyl 2-methylbutanethioate, in particular, is in use for the purpose of providing, for example, an odor of food fermentation or a feeling of ripe fruit.
The flavor component or fragrance component comprising such a racemic S-alkyl 2-methylbutanethioate as an active ingredient is satisfactory to some extent in that it provides a good fermentation odor or a feeling of ripe fruit; however, it is not sufficient. Also, the flavor-improving agent comprising the racemic S-alkyl 2-methylbutanethioate as an active ingredient, still has much room for improvement in release of odor.
Meanwhile, in connection with the analysis of the odorous component of cheese, there was made a chromatographic analysis on S-methyl(S)-2-methylbutanethioate and racemic S-methyl 2-methylbutanethioate, and their odor characteristics were reported (non-patent literature 14). Also, in connection with the analysis of the odorous component of hop, the odor characteristic of racemic S-methyl 2-methylbutanethioate was reported. (non-patent literature 8).
According to the descriptions in these literatures, the odor characteristic of racemic S-methyl 2-methylbutanethioate is wild strawberry (non-patent literature 14), or cooked vegetable, sulphury or soapy/fatty (non-patent literature 8), and the odor characteristic of S-methyl(S)-2-methylbutanethioate is rubbery (non-patent literature 14).
However, none of these reports mentions the odor of S-alkyl(R)-2-methylbutanethioate, such as S-methyl(R)-2-methylbutanethioate. Further, each of these reports evaluated only the odor characteristics of single compounds, having no direct connection with the flavors of beverages or foods, and made no evaluation on the flavors and odor releases when S-alkyl(S)-2-methylbutanethioate had been actually used in beverages or foods (although, in these reports, there are descriptions on S-alkyl(S)-2-methylbutanethioate).    Non-patent literature 1: Food Chemistry (2000), 69 (3), 319-330    Non-patent literature 2: Journal of the Institute of Brewing (1983), 89 (2), 87-91    Non-patent literature 3: Proceedings of the Congress-European Brewery Convention (1981), 18th, 161-8    Non-patent literature 4: Proceedings of the Congress-European Brewery Convention (1979), 17th, 79-89    Non-patent literature 5: Proceedings of the Congress-European Brewery Convention (1981), 17th, 91-104    Non-patent literature 6: Technical Quarterly-Master Brewers Association of the Americas (1981), 18(1), 26-30    Non-patent literature 7: Organic Magnetic Resonance (1979), 12(10), 557-60    Non-patent literature 8: Proceedings of the Analytical Division of the Chemical Society (1976), 13(7), 215-17    Non-patent literature 9: Journal of Organic Chemistry (1973), 38 (24), 4239-43    Non-patent literature 10: Flavour and Fragrance Journal (1996), 11 (5), 295-303    Non-patent literature 11: Tetrahedron Letters (1971), (30), 2837-8    Non-patent literature 12: Development in Food Science (1988), 18 (Flavors Fragrances), 573-85    Non-patent literature 13: Abstrack book of 32nd Symposium on the Chemistry of Terpenes, Essential oils, Aromatics, 31 to 33 pages, Oct. 24, 1988.    Non-patent literature 14: Lebensmittel-Wissenschaft und—Technologie (1979), 12 (5), 258-61